Reading People's Minds

Maths can't really reveal the secret of telepathy (reading people's minds), but some clever maths tricks make it seem like it is possible. Some of these will need a calculator. Examples are in square brackets but try them with other numbers and read people's minds!

The Answer is Three

• Think of a whole number (an integer) bigger than zero [e.g. 4]
• Square it (multiply it by itself) [16]
• Add the original number [20]
• Divide by the original number [5]
• Add 17 [22]
• Take away the original number [18]
• Divide by six [3]
• The answer is always three.

The Answer is Five

• Think of a whole number bigger than zero [e.g. 2]
• Multiply it by two [4]
• Add 10 [14]
• Divide by two [7]
• Take away the original number [5]
• The answer is always five.

Guess Two Numbers

• Pick a number from one to nine [e.g. 8]
• Double it [16]
• Add five [21]
• Multiply by five [105]
• Pick another number from one to nine and add it [e.g. 2 - 107]
• To guess the two numbers, subtract 25 from the total [82] – the first digit is the first number and the second digit is the second number.

The Grey Elephant From Denmark

• Pick a number from five to nine [e.g. 9]
• Take away five [4]
• Multiply by three [12]
• Square the number (multiply it by itself) [144]
• If the answer is higher than ten, add the digits together to get a single number [1+4+4=9).
• If the resulting number is less than five, add five – if it is more than five, subtract four [5]
• Multiply by two [10]
• Subtract six [4]
• Pick the letter of the alphabet that corresponds with the number (e.g. A=1, B=2)
• Pick a country beginning with the letter
• Pick a animal that begins with the second letter of the country
• What colour is the animal?
This doesn't work every time, but most people will be thinking about a grey elephant from Denmark. Why? The answer to the numbers part is always four, so the letter chosen is always 'D'. Most people seem to choose 'Denmark' and a grey elephant.

Guess a Three Digit Number

• Pick a three digit number [e.g. 123]
• Multiply by seven [861]
• Multiply by 11 [9471]
• Multiply by 13 [123123]
• The answer will be the original number twice.

Guess the Date

• Pick a date [e.g. 1 January 2009]
• Add 18 to the chosen month [19]
• Multiply by 25 [475]
• Subtract 333 [142]
• Multiply by eight [1136]
• Subtract 554 [582]
• Divide by two [291]
• Add the chosen day [292]
• Multiply by five [1460]
• Add 692 [2152]
• Multiply by 20 [43040]
• Add the last two digits of the chosen year [43049]
• Subtract 32940 [10109]
• The answer is the date in month/day/year format

Guess the Seven Digit Number

• Pick a seven digit number [e.g. 1234567]
• Multiply the first three digits by 80 [9840]
• Add one [9841]
• Multiply by 250 [2460250]
• Add the last four digits of the chosen number [2464817]
• Add the last four digits of the chosen number again [2469384]
• Subtract 250 [2469134]
• Divide by two [1234567]
• The answer is the original number

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